US4047960A - Refractory partially crystalline materials with good visible transparency - Google Patents

Refractory partially crystalline materials with good visible transparency Download PDF

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US4047960A
US4047960A US05/697,315 US69731576A US4047960A US 4047960 A US4047960 A US 4047960A US 69731576 A US69731576 A US 69731576A US 4047960 A US4047960 A US 4047960A
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Richard F. Reade
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Corning Glass Works
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    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
    • C03C10/00—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition
    • C03C10/0009—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition containing silica as main constituent

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  • the principal objective of the instant invention is to provide a transparent partially crystalline material which, being produced from a glass, can be easily shaped into an envelope for a high temperature lamp, and which resists deformation up to temperatures of 1000° C. and higher.
  • the above objective can be achieved by the controlled heat treatment of glass articles consisting essentially, in weight percent on the oxide basis, of about 10-20% Al 2 O 3 , 59-72% SiO 2 , 5-8% TiO 2 , and 5-20% Nb 2 O 5 and/or Ta 2 O 5 0 to about 2% K 2 O and/or 0 to about 6% Cs 2 O.
  • the method of the invention comprises three general steps. First, a glass-forming batch of a proper composition is melted. Second, the melt is simultaneously cooled to a glass at a temperature at least within the transformation range and an article of a desired configuration shaped therefrom. Third, the glass article is subjected to a temperature between about 1000°-1150° C. to cause the in situ growth of crystals within the glass.
  • the crystallization process is divided into two parts.
  • the glass article is first heated to about 800°-1000° C. to effect substantial nucleation within the glass and, subsequently, the nucleated glass is heated to about 1000°-1150° C. to cause the growth of crystals on the nuclei.
  • the materials contain a substantial crystal content homogeneously dispersed within a residual glassy matrix, the crystals generally constituting at least about 20%, but less than about 50% by volume, of the materials.
  • Aluminum niobate, aluminum tantalate, or an aluminum niobate-tantalate solid solution comprises the predominant crystal phase.
  • the crystals are much smaller in size than the wavelength of visible light, being only about 300-500A in diameter.
  • the materials exhibit coefficients of thermal expansion over the range of room temperature (R.T.) to 1000° C. of less than about 30 ⁇ 10 -7 / ° C. and can demonstrate a high degree of transparency to visible light, particularly within the range of 4500-7500A, which is retained even after extended exposures to temperatures up to 1000° C.
  • TiO 2 functions as a flux, enabling the glass batch to be melted at temperatures of about 1650°-1700° C. Without the presence of TiO 2 , temperatures in excess of 1800° C. would be required for melting the batch, thereby foreclosing the use of conventional glass melting facilities and practies.
  • Substantial opacity is developed within a relatively brief time at temperatures of 1200° C. and higher.
  • the presence of mullite and/or cristobalite causes the coefficient of thermal expansion over the range of R.T. to 1000° C. to rise about 30 ⁇ 10 -7 /° C.
  • the inclusion of up to about 2% K 2 O and/or up to about 6% Cs 2 O can be advantageous in inhibiting the growth of cristobalite.
  • the presence of cristobalite causes a marked increase in the coefficient of thermal expansion of the materials.
  • the extensive growth of cristobalite during exposure to high temperatures can lead to cracking and spalling of the surface as the crystallized article is cooled to room temperature.
  • Table I records compositions, expressd in parts by weight on the oxide basis, that are useful in the instant invention. Inasmuch as the sum of the various ingredients approximates 100 in each example, the individual values can, for all practical purposes, be deemed to be reported in percent by weight.
  • the actual batch ingredients can comprise any materials, either the oxide or other compound, which, when melted together, will convert to the desired oxide in the proper proportions.
  • the batch materials were compounded, ballmilled together to aid in securing a homogeneous melt, and run into platinum crucibles. After placing a lid thereon, the crucibles were inserted into an electrically-fired furnace operating at about 1700° C. and held therein for about 16 hours. The melts were poured into a steel mold to yield glass slabs about 6 ⁇ 6 ⁇ 1/2 inch and the slabs immediately transferred to an annealer operating at about 700° C. Upon completion of annealing, samples were cut from each slab in the proper geometry for physical property measurements to be conducted thereon. As 2 O 3 was included in its conventional function as a fining agent.
  • the heat treatment step is time and temperature dependent. Thus, at the higher extreme of the 1000° C., but no higher than about 1150° C., range, an exposure of 1-4 hours may be sufficient to insure the growth of aluminum niobate and/or aluminum tantalate crystals, whereas at the cooler extreme 24-48 hours may be required.
  • the glass bodies were annealed to room temperature to permit inspection of glass quality and for ease in cutting test samples. Such is not a mandatory practice. All that is required is that the melt be cooled to at least within the transformation range to produce an essentially crystal-free glass, and then the glass reheated to cause crystallization in situ.
  • the transformation range has generally been defined as that temperature at which a molten mass is converted into an amorphous body, this temperature commonly being considered to lie in the vicinity of the annealing point of the glass.
  • Table II records heat treatments applied to the compositions of Table I along with a visual description of the crystalline product, a definition of the crystal phases present as identified through X-ray diffraction analyses, coefficients of thermal expansion over the range of R.T. to 1000° C. ( ⁇ 10 31 7 /° C.), as determined in accordance with conventional measuring techniques, and the transmittance to visible light having a wavelength of 5500° C., measured spectrophotometrically through polished samples 1 mm. or 2 mm. thick as crystallized examples and after exposure to 1010° C. for 200 or 500 hours. In each instance an electrically-fired furnace was employed and the temperature thereof raised at a rate of about 100° -300° C./hour to the hold temperatures reported.
  • the crystalline bodies were cooled to room temperature by merely cutting off the electricity to the furnace and allowing the furnace to cool with the bodies retained therein. This rate of cooling was estimated to average about 3°-5° C./minute. Since the coefficient of thermal expansion of the transparent crystalline bodies is quite low, commonly about 20-25 ⁇ 10 -7 / ° C., much more rapid rates of cooling are obviously operable. This "cooling at furnace rate" is a matter of convenience in the laboratory.
  • the preferred compositions for the transparent materials consist essentially solely of the quaternary Nb 2 O 5 and/or Ta 2 O 5 --Al 2 O 3 --SiO 2 --TiO 2 , since additions of other ingredients can have an adverse effect upon transparency and/or refractoriness. This is particularly true of such conventional fluxing agents as the alkali metal oxides, B 2 O 3 , P 2 O 5 , and fluoride. Therefore, the preferred compositions will be essentially free from such ingredients. Likewise, such divalent metal oxides as the alkaline earths and PbO, which can form unwanted secondary crystal phases, will preferably be absent. Up to 2% K 2 O and/or up to 6% Cs 2 O may be added to inhibit cristobalite formation. In sum, the total of all extraneous oxides, if present, will not exceed about 8% by weight.
  • rutile in Examples 8 and 10-16 is not positive but the phase may be (1) TiO 2 , (2) a form of aluminum tantalate, or (3) a solid solution of these two.
  • the X-ray patterns of rutile, a tetragonal form of TiO 2 , and that of the tetragonal form of AlTaO 4 are substantially identical.
  • Al +3 and Ta +5 ions occupy alternate positions in the crystal lattice in a manner similar to those occupied by Ti +4 ions in rutile.
  • the identification of AlTaO 4 in Table II refers to the orthorhombic form thereof.

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  • Ceramic Engineering (AREA)
  • Crystallography & Structural Chemistry (AREA)
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Abstract

This invention is concerned with the manufacture of refractory articles of a partially crystalline nature, i.e., materials having a substantial crystal content within a glassy matrix, but wherein the crystal phase normally comprises less than about 50% by volume of the materials. The bodies are produced through the heat treatment of glass articles having compositions within the Al2 O3 --SiO2 --TiO2 --Nb2 O5 and/or Ta2 O5 system at elevated temperatures, but not in excess of about 1150° C., to cause the in situ growth of crystals. The materials, containing aluminum niobate, aluminum tantalate, or an aluminum niobate-tantalate solid solution as the predominant crystal phase, exhibit a high degree of transparency to visible light, and retain that transparency even after very extended exposures to temperatures up to in excess of 1000° C. That capability has recommended their utility as arc-tubes or as envelopes for high temperature lamps.

Description

OBJECTIVE OF THE INVENTION
The use of high temperature lamps has steadily increased in recent years, particularly for highway and other outdoor lighting purposes. Since the efficiency of such lamps increases with higher temperatures, there has been a real need for transparent materials capable of withstanding temperatures of 1000° C. and higher without deformation. Fused quartz and sintered alumina materials have been and are being employed for such applications, but these are very expensive and difficult to form.
Therefore, the principal objective of the instant invention is to provide a transparent partially crystalline material which, being produced from a glass, can be easily shaped into an envelope for a high temperature lamp, and which resists deformation up to temperatures of 1000° C. and higher.
SUMMARY OF THE INVENTION
The above objective can be achieved by the controlled heat treatment of glass articles consisting essentially, in weight percent on the oxide basis, of about 10-20% Al2 O3, 59-72% SiO2, 5-8% TiO2, and 5-20% Nb2 O5 and/or Ta2 O5 0 to about 2% K2 O and/or 0 to about 6% Cs2 O. The method of the invention comprises three general steps. First, a glass-forming batch of a proper composition is melted. Second, the melt is simultaneously cooled to a glass at a temperature at least within the transformation range and an article of a desired configuration shaped therefrom. Third, the glass article is subjected to a temperature between about 1000°-1150° C. to cause the in situ growth of crystals within the glass. In the preferred practice to attain a more dense and more uniformly-sized crystallization, the crystallization process is divided into two parts. Thus, the glass article is first heated to about 800°-1000° C. to effect substantial nucleation within the glass and, subsequently, the nucleated glass is heated to about 1000°-1150° C. to cause the growth of crystals on the nuclei.
The materials contain a substantial crystal content homogeneously dispersed within a residual glassy matrix, the crystals generally constituting at least about 20%, but less than about 50% by volume, of the materials. Aluminum niobate, aluminum tantalate, or an aluminum niobate-tantalate solid solution comprises the predominant crystal phase. The crystals are much smaller in size than the wavelength of visible light, being only about 300-500A in diameter.
The materials exhibit coefficients of thermal expansion over the range of room temperature (R.T.) to 1000° C. of less than about 30 × 10-7 / ° C. and can demonstrate a high degree of transparency to visible light, particularly within the range of 4500-7500A, which is retained even after extended exposures to temperatures up to 1000° C.
TiO2 functions as a flux, enabling the glass batch to be melted at temperatures of about 1650°-1700° C. Without the presence of TiO2, temperatures in excess of 1800° C. would be required for melting the batch, thereby foreclosing the use of conventional glass melting facilities and practies.
Extended exposures of the transparent materials to temperatures above 1150° C. cause the development of translucency therewithin. This phenomenon results from the growth in situ of mullite and/or cristobalite crystals in addition to the aluminum niobate and/or tantalate. The materials become opaque due to increased crystallinity (in excess of 50% by volume) and the larger size of the mullite and/or cristobalite crystals, i.e., greater than the wavelength of visible light.
Substantial opacity is developed within a relatively brief time at temperatures of 1200° C. and higher. In addition, the presence of mullite and/or cristobalite causes the coefficient of thermal expansion over the range of R.T. to 1000° C. to rise about 30 × 10-7 /° C.
The inclusion of up to about 2% K2 O and/or up to about 6% Cs2 O can be advantageous in inhibiting the growth of cristobalite. The presence of cristobalite causes a marked increase in the coefficient of thermal expansion of the materials. The extensive growth of cristobalite during exposure to high temperatures can lead to cracking and spalling of the surface as the crystallized article is cooled to room temperature.
DESCRIPTION OF PREFERRED EMBODIMENTS
Table I records compositions, expressd in parts by weight on the oxide basis, that are useful in the instant invention. Inasmuch as the sum of the various ingredients approximates 100 in each example, the individual values can, for all practical purposes, be deemed to be reported in percent by weight. The actual batch ingredients can comprise any materials, either the oxide or other compound, which, when melted together, will convert to the desired oxide in the proper proportions.
The batch materials were compounded, ballmilled together to aid in securing a homogeneous melt, and run into platinum crucibles. After placing a lid thereon, the crucibles were inserted into an electrically-fired furnace operating at about 1700° C. and held therein for about 16 hours. The melts were poured into a steel mold to yield glass slabs about 6 × 6 × 1/2 inch and the slabs immediately transferred to an annealer operating at about 700° C. Upon completion of annealing, samples were cut from each slab in the proper geometry for physical property measurements to be conducted thereon. As2 O3 was included in its conventional function as a fining agent.
              TABLE I                                                     
______________________________________                                    
        1        2        3      4      5                                 
______________________________________                                    
SiO.sub.2                                                                 
        68.0     70.5     69.2   64.6   66.8                              
Al.sub.2 O.sub.3                                                          
        16.5     15.0     14.7   15.7   14.2                              
Nb.sub.2 O.sub.5                                                          
        8.6      7.8      7.7    10.9   7.4                               
TiO.sub.2                                                                 
        6.9      6.3      6.1    6.5    5.9                               
As.sub.2 O.sub.3                                                          
        0.4      0.5      0.5    0.5    0.5                               
K.sub.2 O                                                                 
        --       --       1.8    1.9    --                                
Cs.sub.2 O                                                                
        --       --       --     --     5.2                               
        6        7        8      9      10                                
______________________________________                                    
SiO.sub.2                                                                 
        62.2     63.5     62.3   60.1   64.4                              
Al.sub.2 O.sub.3                                                          
        15.1     15.4     15.1   14.6   15.6                              
Nb.sub.2 O.sub.5                                                          
        10.5     5.4      5.3    5.1    --                                
Ta.sub.2 O.sub.5                                                          
        --       8.9      8.7    8.4    13.5                              
TiO.sub.2                                                                 
        6.2      6.4      6.3    6.1    6.5                               
As.sub.2 O.sub.3                                                          
        0.5      0.5      0.5    0.5    0.4                               
K.sub.2 O                                                                 
        --       --       1.9    --     --                                
Cs.sub.2 O                                                                
        5.6      --       --     5.4    --                                
        11       12       13     14     15                                
______________________________________                                    
SiO.sub.2                                                                 
        67.1     63.0     61.6   67.4   65.7                              
Al.sub.2 O.sub.3                                                          
        14.2     17.3     14.9   14.3   13.8                              
Ta.sub.2 O.sub.5                                                          
        12.3     13.2     17.2   12.4   13.8                              
TiO.sub.2                                                                 
        5.9      6.4      6.2    6.0    6.7                               
As.sub.2 O.sub.3                                                          
        0.5      0.4      0.4    0.4    0.4                               
______________________________________
The heat treatment step is time and temperature dependent. Thus, at the higher extreme of the 1000° C., but no higher than about 1150° C., range, an exposure of 1-4 hours may be sufficient to insure the growth of aluminum niobate and/or aluminum tantalate crystals, whereas at the cooler extreme 24-48 hours may be required. In the laboratory examples discussed above, the glass bodies were annealed to room temperature to permit inspection of glass quality and for ease in cutting test samples. Such is not a mandatory practice. All that is required is that the melt be cooled to at least within the transformation range to produce an essentially crystal-free glass, and then the glass reheated to cause crystallization in situ. The transformation range has generally been defined as that temperature at which a molten mass is converted into an amorphous body, this temperature commonly being considered to lie in the vicinity of the annealing point of the glass.
Table II records heat treatments applied to the compositions of Table I along with a visual description of the crystalline product, a definition of the crystal phases present as identified through X-ray diffraction analyses, coefficients of thermal expansion over the range of R.T. to 1000° C. (×1031 7 /° C.), as determined in accordance with conventional measuring techniques, and the transmittance to visible light having a wavelength of 5500° C., measured spectrophotometrically through polished samples 1 mm. or 2 mm. thick as crystallized examples and after exposure to 1010° C. for 200 or 500 hours. In each instance an electrically-fired furnace was employed and the temperature thereof raised at a rate of about 100° -300° C./hour to the hold temperatures reported. It will be appreciated, of course, that no hold temperature, as such, is required; such is only a matter of convenience. All that is necessary is the exposure of the precursor glass body to temperatures within the 1000°-1150° C. range. The rate at which the glass temperature is raised is governed by the tendency of the body to deform or slump. Where formers or other physical supports are employed, rates of 10° C./minute and faster may be utilized. Heat treatments up to 100° C. which yield opaque, fine-grained bodies are included for comparison.
In each instance, the crystalline bodies were cooled to room temperature by merely cutting off the electricity to the furnace and allowing the furnace to cool with the bodies retained therein. This rate of cooling was estimated to average about 3°-5° C./minute. Since the coefficient of thermal expansion of the transparent crystalline bodies is quite low, commonly about 20-25 × 10-7 / ° C., much more rapid rates of cooling are obviously operable. This "cooling at furnace rate" is a matter of convenience in the laboratory.
However, it is believed that both the rate of heating the glass article to effect crystallization and the rating of cooling the crystallized body to room temperature are well within the technical ingenuity of the person of ordinary skill in the art.
                                  TABLE II                                
__________________________________________________________________________
Example                  Crystal Coef.                                    
                                     % Transmittance at 5500A°     
No.  Heat Treatment                                                       
                 Description                                              
                         Phases  Exp.                                     
                                     Thickness                            
                                           As Crystallized                
                                                     1010°         
                                                          Hours           
__________________________________________________________________________
 1   300° C/hr to 850° C,                                   
                 Transparent,                                             
                         Aluminum                                         
                                 24.0                                     
                                     2 mm. 74%       --   --              
     Hold for 2 hours,                                                    
                 very slight                                              
                         niobate                                          
     200° hazer to 1000° C,                                 
     Hold for 2 hours                                                     
     200° C/hr to 1100° C,                                  
     Hold for 16 hours                                                    
 1   300° C/hr to 850° C,                                   
                 White, opaque                                            
                         Cristobalite                                     
                                 --  --    --        --   --              
     Hold for 2 hours    Mullite,                                         
     200° C/hr to 1000° C,                                  
                         Aluminum                                         
     Hold for 2 hours    niobate                                          
     200° C/hr to 1200° C,                                  
     Hold for 16 hours                                                    
 2   300° C/hr to 850° C,                                   
                 Transparent,                                             
                         Aluminum                                         
                                 20.4                                     
                                     2 mm. 77%       76%  200             
     Hold for 2 hours                                                     
                 very slight                                              
                         niobate                                          
     200° C/hr to 1000° C,                                  
                 haze                                                     
     Hold for 2 hours                                                     
     200° C/hr to 1100° C,                                  
     Hold for 16 hours                                                    
 2   300° C/hr to 1000° C                                   
                 Gray, opaque                                             
                         Cristobalite,                                    
                                 --  --    --        --   --              
     Hold for 4 hours    Mullite,                                         
     200° C/hr to 1200° C.                                  
                         Aluminum                                         
     Hold for 4 hours    niobate                                          
 3   300° C/hr to 850° C.                                   
                 Transparent,                                             
                         Aluminum                                         
                                 --  2 mm. 71%       --   --              
     Hold for 2 hours                                                     
                 slight haze                                              
                         niobate                                          
     200° C/hr to 100° C                                    
     Hold for 2 hours                                                     
     200° C/hr to 1100° C                                   
     Hold for 16 hours                                                    
 3   300° C/hr to 100° C                                    
                 Gray, opaque                                             
                         Cristobalite,                                    
                                 --  --    --        --   --              
     Hold for 4 hours    Mullite,                                         
     200° C/hr to 1200° C                                   
                         Aluminum                                         
     Hold for 4 hours    niobate                                          
 4   300° C/hr to 850° C.                                   
                 Transparent-                                             
                         Aluminum                                         
                                 --  2 mm. 63%       --   --              
     Hold for 2 hours                                                     
                 to-translucent                                           
                         niobate                                          
     200° C/hr to 1000° C                                   
     Hold for 2 hours                                                     
     200° C/hr to 1100° C                                   
     Hold for 16 hours                                                    
 5      "        Transparent                                              
                           "     --  2 mm. 81%       80%  200             
 5   200° C/hr to 1050° C                                   
                 Transparent                                              
                         Aluminum                                         
                                 23.7                                     
                                     1 mm. 86%       83%  500             
     Hold for 4 hours    niobate                                          
     100° C/hr to 1150° C                                   
     Hold for 4 hours                                                     
 6   300° C/hr to 850° C.                                   
                 Transparent,                                             
                         Aluminum                                         
                                 --  2 mm. 69%       --   --              
     Hold for 2 hours                                                     
                 slight haze                                              
                         niobate                                          
     200° C/hr to 1000° C                                   
     Hold for 2 hours                                                     
     200° C/hr to 1100° C                                   
     Hold for 16 hours                                                    
 6   200° C/hr to 1050° C                                   
                 Transparent,                                             
                         Aluminum                                         
                                 27.2                                     
                                     1 mm. 80%       76%  f 500           
     Hold for 4 hours                                                     
                 slight haze                                              
                         niobate                                          
     100° C/hr to 1150° C                                   
     Hold for 4 hours                                                     
 7   300° C/hr to 850° C                                    
                 Transparent,                                             
                         Aluminum                                         
                                 24.4                                     
                                     --    --        --   --              
     Hold for 2 hours                                                     
                 slight haze                                              
                         niobate-                                         
     200° C/hr to 1000° C                                   
                         tantalate                                        
     Hold for 2 hours    solid                                            
     200° C/hr to 1100° C                                   
                         solution                                         
     Hold for 16 hours                                                    
 8      "        Transparent-                                             
                         Aluminum                                         
                                 --  2 mm. 52%       --   --              
                 to-translucent                                           
                         niobate-                                         
                         tantalate solid                                  
                         solution, Rutile                                 
 9   300° C/hr to 850° C                                    
                 Transparent,                                             
                         Aluminum                                         
                                 --  2 mm. 77%       71%  200             
     Hold for 2 hours                                                     
                 slight haze                                              
                         niobate-                                         
     200° C/hr to 1000° C                                   
                         tantalate                                        
     Hold for 2 hours    solid                                            
     200° C/hr to 1100° C                                   
                         solution                                         
     Hold for 16 hours                                                    
 9   200° C/hr to 1050° C                                   
                 Transparent                                              
                           "     27.2                                     
                                     1 mm. 84%       81%  500             
     Hold for 4 hours                                                     
     1000° C/hr to 1150° C                                  
     Hold for 4 hours                                                     
 9   300° C/hr to 1000° C                                   
                 Gray, opaque                                             
                         Cristobalite,                                    
                                 --  --    --        --   --              
     Hold for 4 hours    Aluminum                                         
     200° C/hr to 1200° C                                   
                         niobate-                                         
     Hold for 4 hours    tantalate                                        
                         solid solution                                   
10   300° Transparent0° C                                   
                         Aluminum                                         
                                 24.6                                     
                                     --    --        --   --              
     Hold for 2 hours                                                     
                 slight haze                                              
                         tantalate,                                       
     200° C/hr to 1000° C                                   
                         Rutile                                           
     Hold for 2 hours                                                     
     200° C/hr to 1100° C                                   
     Hold for 16 hours                                                    
10   300° C/hr to 850° C                                    
                 White, opaque                                            
                         Cristobalite                                     
                                 --  --    --        --   --              
     Hold for 2 hours                                                     
                 Mullite,                                                 
     200° C/hr to 1000° C                                   
                         Aluminum                                         
     Hold for 2 hours    tantalate,                                       
     200° C/hr to 1200° C                                   
                         Rutile                                           
     Hold for 16 hours                                                    
11   300° C/hr to 850° C                                    
                 Transparent,                                             
                         Aluminum                                         
                                 24.1                                     
                                     2 mm. 76%       72%  200             
     Hold for 2 hours                                                     
                 very slight                                              
                         tantalate,                                       
     200° C/hr to 1000° C                                   
                 haze    Rutile                                           
     Hold for 2 hours                                                     
     200° C/hr to 1100° C                                   
     Hold for 16 hours                                                    
11   300° C/hr to 1000° C                                   
                 Gray, trans-                                             
                         Cristobalite,                                    
                                 --  --    --        --   --              
     Hold for 4 hours                                                     
                 lucent-to-                                               
                         Alumimum                                         
     200° C/hr to 1200° C                                   
                 opaque  tantalate,                                       
     Hold for 4 hours    Rutile                                           
12   300° C/hr to 850° C                                    
                 Transparent,                                             
                         Aluminum                                         
                                 --  --    --        --   '               
     Hold for 2 hours                                                     
                 very slight                                              
                         tantalate                                        
     200° C/hr to 1000° C                                   
                 haze    Rutile                                           
     Hold for 2 hours                                                     
     200° C/hr to 1100° C                                   
     Hold for 16 hours                                                    
13      "          "       "     --  --    --        --   --              
14      "        Transparent                                              
                           "     --  --    --        --   --              
15      "          "       "     --  --    --        --   --              
__________________________________________________________________________
Table II clearly illustrates the criticality of heat treatment temperature required to assure the production of transparent articles. The preferred compositions for the transparent materials consist essentially solely of the quaternary Nb2 O5 and/or Ta2 O5 --Al2 O3 --SiO2 --TiO2, since additions of other ingredients can have an adverse effect upon transparency and/or refractoriness. This is particularly true of such conventional fluxing agents as the alkali metal oxides, B2 O3, P2 O5, and fluoride. Therefore, the preferred compositions will be essentially free from such ingredients. Likewise, such divalent metal oxides as the alkaline earths and PbO, which can form unwanted secondary crystal phases, will preferably be absent. Up to 2% K2 O and/or up to 6% Cs2 O may be added to inhibit cristobalite formation. In sum, the total of all extraneous oxides, if present, will not exceed about 8% by weight.
Although the transmittances thereof were not measured spectrophotometricallly, Examples 1, 10, 12, and 13, when subjected to a top heat treatment temperature of 1100° C., evidenced neither a visible loss of transmittance nor physical deformation and slumping after an exposure of 350 hours at a temperature of 1010° C.
The identification of "rutile" in Examples 8 and 10-16 is not positive but the phase may be (1) TiO2, (2) a form of aluminum tantalate, or (3) a solid solution of these two. The X-ray patterns of rutile, a tetragonal form of TiO2, and that of the tetragonal form of AlTaO4 are substantially identical. In the latter phase, Al+3 and Ta+5 ions occupy alternate positions in the crystal lattice in a manner similar to those occupied by Ti+4 ions in rutile. The identification of AlTaO4 in Table II refers to the orthorhombic form thereof.

Claims (3)

I claim:
1. A method for making a transparent partially crystalline article containing at least about 20%, but less than about 50%, by volume crystals dispersed within a residual glassy matrix wherein the predomininant crystal phase consists essentially of aluminum niobate, aluminum tantalate, or an aluminum-tantalate solid solution having a crystal size of about 300-500A in diameter, which crystalline article retains its transparency after extended exposures to temperatures up to about 1150° C., comprising the steps of:
a. melting a batch for a glass consisting essentially, in weight percent on the oxide basis, of about 10-20% Al2 O3, 59-72% SiO2, 5-8% TiO2, and 5-20% Nb2 O5 and/or Ta2 O5 0 to about 2% K2 O and/or 0 to about 6% Cs2 O;
b. simultaneously cooling said melt to a temperature at least within the transformation range and shaping a glass article of a desired configuration therefrom;
c. heating said glass article to a temperature of at least about 1000° c., but not more than about 1150° C., for a period of time sufficient to cause the crystallization of aluminum niobate, aluminum tantalate, and/or an aluminum niobate-tantalate solid solution having a crystal size of about 300-500A to occur in situ to produce a transparent partially crystalline article; and then
d. cooling said crystallized article to room temperature.
2. A method according to claim 1 wherein said glass article is first heated to about 800°-1000° C. for a period of time sufficient to effect substantial nucleation within said glass prior to heating to crystallize the glass article in situ.
3. A transparent partially crystalline article made in accordance with claim 1.
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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4162921A (en) * 1977-01-05 1979-07-31 Firsov Vitaly M Glass-crystalline material and method of producing same
FR2419922A1 (en) * 1978-03-16 1979-10-12 Owens Illinois Inc POLYCRYSTALLINE CERAMICS FORMED FROM MELTED MASSES AND DOPING HOSTS CONTAINING PHOSPHORUS
US4930731A (en) * 1987-05-06 1990-06-05 Coors Porcelain Company Dome and window for missiles and launch tubes with high ultraviolet transmittance
US4983555A (en) * 1987-05-06 1991-01-08 Coors Porcelain Company Application of transparent polycrystalline body with high ultraviolet transmittance
US5001093A (en) * 1987-05-06 1991-03-19 Coors Porcelain Company Transparent polycrystalline body with high ultraviolet transmittance
US5244849A (en) * 1987-05-06 1993-09-14 Coors Porcelain Company Method for producing transparent polycrystalline body with high ultraviolet transmittance
US6268303B1 (en) 1998-07-06 2001-07-31 Corning Incorporated Tantalum containing glasses and glass ceramics
DE102004024017A1 (en) * 2004-05-13 2005-12-01 Schott Ag Production of illumination device with at least one body enclosing an illuminant useful for automobile illumination, e.g. halogen lamps, miniaturized glass-ceramic devices, and high pressure discharge lamps
US20080227616A1 (en) * 2004-01-05 2008-09-18 Ulrich Peuchert Use of Glass Ceramics
US11168020B2 (en) 2018-02-14 2021-11-09 Corning Incorporated Transparent tantalum oxide glass-ceramics and transparent aluminum tantalate glass-ceramics

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US3732116A (en) * 1970-10-21 1973-05-08 Corning Glass Works Glass-ceramic articles containing strontia-,yttria-,lanthana-,and/or tantala-bearing crystal species
US3839053A (en) * 1973-05-11 1974-10-01 Corning Glass Works Highly opaque, ta205-containing glass-ceramic articles
US3951670A (en) * 1975-02-10 1976-04-20 Corning Glass Works Cristobalite suppression in high-silica Li2 O-Al2 O-SiO2 devitrified glass frits
US3977886A (en) * 1971-07-01 1976-08-31 Jenaer Glaswerk Schott & Gen. Transparent glass ceramic with small thermal expansion
US3984251A (en) * 1971-08-05 1976-10-05 Owens-Illinois, Inc. Glasses of the Na2 0--T2 05 --SiO2 and the Na2 0--L2 0--a2 05 --SiO2 system

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Publication number Priority date Publication date Assignee Title
US3732116A (en) * 1970-10-21 1973-05-08 Corning Glass Works Glass-ceramic articles containing strontia-,yttria-,lanthana-,and/or tantala-bearing crystal species
US3977886A (en) * 1971-07-01 1976-08-31 Jenaer Glaswerk Schott & Gen. Transparent glass ceramic with small thermal expansion
US3984251A (en) * 1971-08-05 1976-10-05 Owens-Illinois, Inc. Glasses of the Na2 0--T2 05 --SiO2 and the Na2 0--L2 0--a2 05 --SiO2 system
US3839053A (en) * 1973-05-11 1974-10-01 Corning Glass Works Highly opaque, ta205-containing glass-ceramic articles
US3951670A (en) * 1975-02-10 1976-04-20 Corning Glass Works Cristobalite suppression in high-silica Li2 O-Al2 O-SiO2 devitrified glass frits

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4162921A (en) * 1977-01-05 1979-07-31 Firsov Vitaly M Glass-crystalline material and method of producing same
FR2419922A1 (en) * 1978-03-16 1979-10-12 Owens Illinois Inc POLYCRYSTALLINE CERAMICS FORMED FROM MELTED MASSES AND DOPING HOSTS CONTAINING PHOSPHORUS
US4930731A (en) * 1987-05-06 1990-06-05 Coors Porcelain Company Dome and window for missiles and launch tubes with high ultraviolet transmittance
US4983555A (en) * 1987-05-06 1991-01-08 Coors Porcelain Company Application of transparent polycrystalline body with high ultraviolet transmittance
US5001093A (en) * 1987-05-06 1991-03-19 Coors Porcelain Company Transparent polycrystalline body with high ultraviolet transmittance
US5244849A (en) * 1987-05-06 1993-09-14 Coors Porcelain Company Method for producing transparent polycrystalline body with high ultraviolet transmittance
US6268303B1 (en) 1998-07-06 2001-07-31 Corning Incorporated Tantalum containing glasses and glass ceramics
US20080227616A1 (en) * 2004-01-05 2008-09-18 Ulrich Peuchert Use of Glass Ceramics
DE102004024017A1 (en) * 2004-05-13 2005-12-01 Schott Ag Production of illumination device with at least one body enclosing an illuminant useful for automobile illumination, e.g. halogen lamps, miniaturized glass-ceramic devices, and high pressure discharge lamps
US11168020B2 (en) 2018-02-14 2021-11-09 Corning Incorporated Transparent tantalum oxide glass-ceramics and transparent aluminum tantalate glass-ceramics
US11708298B2 (en) 2018-02-14 2023-07-25 Corning Incorporated Transparent tantalum oxide glass-ceramics and transparent aluminum tantalate glass-ceramics

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